Air conditioning and refrigeration systems, both stationary and transport types, with transport types including those used on straight trucks, tractor-trailer combinations, and refrigerated containers, conventionally utilize a chlorofluorocarbon (CFC) refrigerant in a mechanical refrigeration cycle. The mechanical refrigeration cycle requires a refrigerant compressor driven by a prime mover, which often includes an internal combustion engine, such as a diesel engine. Because of the suspected depleting effect of CFC's on stratospheric ozone (O.sub.3), practical alternatives to the use of CFC's in refrigeration are being sought.
The use of a cryogen, i.e., a gas which has been compressed to a very cold liquid state, such as carbon dioxide (CO.sub.2) and nitrogen (N.sub.2), in air conditioning and refrigeration systems is particularly attractive because, in addition to eliminating the need for a CFC, it also eliminates the need for a compressor and associated prime mover.
Thus, it would be desirable, and it is an object of the present invention, to provide reliable, practical methods and apparatus which utilize a cryogen in air conditioning and refrigeration systems.